Aqueous wax emulsions and dispersions and uses thereof

ABSTRACT

An aqueous wax emulsion or dispersion comprising, wax, water and an emulsifier wherein the emulsifier comprises purified kraft lignin and a water-soluble base. A process for preparing said aqueous wax dispersions and their use.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under the Paris Convention toU.S. Application No. 62/891,519, filed on Aug. 26, 2019. The content ofsuch prior application is incorporated herein by reference as if setforth in its entirety.

FIELD OF THE INVENTION

In one aspect, the present invention relates to an aqueous waxformulation for use in the manufacture of composite wood panels andmethods of formulating same. More specifically, the aqueous waxformulation is an aqueous wax emulsion or an aqueous wax dispersion foruse in the manufacture of composite wood panels and methods offormulating same. More specifically, an aqueous wax emulsion or aqueouswax dispersion including lignin and a base as an emulsifying agent.

BACKGROUND OF THE INVENTION

The manufacture of wood based panels such as particleboard, fibreboard(MDF, HDF and OSB) and the like (collectively referred to herein as“composite wood panels”) generally comprises a first step of combiningwood chips or particles and an adhesive. The mixture is then formed intoa mat, which is then heated under pressure to cure the adhesive and toform the desired panel. Formaldehyde based resins, such asurea-formaldehyde (UF), are typical adhesives used in the manufacture ofsuch panels. Other types of resins not containing UF may also be used.

In order to impart water repelling, or hydrophobing, characteristics tocomposite wood panels, it is known to include a wax component into thepanel manufacturing process. Thus, once the panel is made, thehydrophobic component serves to repel water from being absorbed, therebypreventing deterioration of the panel. Additionally, the presence of waximproves the ease of manufacturing of composite wood panels.

Aqueous wax emulsions and dispersions are known for use in themanufacture of composite wood panels. Generally, manufacture of aqueouswax emulsions and dispersions comprises the emulsification of molten waxwith an aqueous phase containing an emulsifier under high shear. In thecase of dispersions the emulsified molten wax and aqueous phase areallowed to cool below the wax melting point temperature. The emulsifiermay consist of an alkyl fatty acid in combination with a complementaryorganic base, as is for example described in U.S. Pat. No. 2,349,326.Additionally, other emulsifiers may be used as disclosed inWO2010053494A1 or U.S. Pat. No. 7,842,731 B1, comprising lignosulfonate.

It has been well understood that the presence of an emulsifier isnecessary to produce an aqueous wax dispersion, and to providesufficient stability for the aqueous wax dispersion to be useful in theintended application. However, presence of an emulsifier adverselyaffects some other characteristics of the aqueous wax dispersion. Forexample, the use of an emulsifier may induce foaming or impede the waterrepellent performance of the wax. With increased loading of theseemulsifiers, foaming typically increases and water repellant performancetypically deteriorates. The use of an emulsifier in an aqueous waxdispersion thus constitutes a trade-off between the aqueous waxdispersion stability and its performance. Emulsifiers known in the artfor the manufacture of aqueous wax dispersions are generally used at alevel that provides an acceptable comprise between stability andperformance. This compromise thus sacrifices water repellent performancein order to achieve sufficient aqueous wax dispersion stability forproduction, transport, storage, and use. Emulsifiers are also used inthe manufacture of aqueous wax emulsions to provide sufficient stabilityfor the emulsions to be useful in the intended application. The use ofemulsifiers in the manufacture of aqueous wax emulsions results insimilar trade-offs to those described for dispersions.

As a result, there is a need in the art for emulsifiers for aqueous waxemulsions and dispersions combining excellent aqueous wax emulsion ordispersion stability without compromising moisture repellent performanceof wax in composite wood panels.

SUMMARY OF THE INVENTION

It has been found that lignin in the presence of a water-soluble basecan act as an emulsifying agent in an aqueous wax emulsion or an aqueouswax dispersion. Accordingly, in one aspect of the application there isprovided an aqueous wax formulation which may be an aqueous wax emulsionor an aqueous wax dispersion comprising a wax, water, and an emulsifiercomprising lignin and a water-soluble base.

In another aspect of the application there is provided a method ofproducing an aqueous wax emulsion comprising i) preparing an aqueousphase containing an emulsifier comprising lignin and a water-solublebase; ii) emulsifying molten wax with the aqueous phase. The method mayfurther comprises the optional step of keeping or storing the aqueouswax emulsion at a temperature above the congealing point of the wax andunder gentle agitation.

In another aspect of the application there is provided a method ofproducing an aqueous wax dispersion comprising i) preparing an aqueousphase containing an emulsifier comprising lignin and a water-solublebase; ii) emulsifying molten wax with the aqueous phase and iii) coolingto below the congealing point of the wax to form the aqueous waxdispersion.

In a further aspect of the application there is provided a use of anaqueous wax emulsion or dispersion as described above in the manufactureof composite wood panels.

In yet a further aspect of the application there is provided a method ofmanufacturing a composite wood panel comprising the steps of (i)blending lignocellulosic material in the presence of an adhesive resinand an aqueous wax emulsion or aqueous wax dispersion as describedabove, (ii) forming the blended lignocellulosic material containingadhesive and aqueous wax emulsion or aqueous wax dispersion, and (iii)consolidating the formed lignocellulosic material using pressure andtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (prior art) is a chart showing commercially available purifiedKraft lignins.

FIG. 2 is a graph showing the relative lignin solubility as a functionof the equivalent base mass ratio for a strong base and for weak basesof different pKa.

FIG. 3 is a flow chart depicting exemplary embodiments of aqueous waxdispersion compositions comprising lignin as an emulsifier.

FIG. 4 is a graph comparing percentage of lignin solubility as afunction of the equivalent mass ratio of base to lignin for differentbases. The curves shown represent a best fit of the experimental dataaccording to Equation 1. Data points have been omitted for clarityreasons.

FIG. 5 is a graph showing the minimum equivalent mass ratio of base tolignin value as a function of base pKa for 7 bases. The pKa values inthe graph were obtained from Rayer, A. V., Sumon, K. A., Jaffari L/andHenni, A., Dissociation constants (pKa) of tertiary and cyclic amines:Structural and temperature dependencies, Journal of Chemical andEngineering Data 59(11) 3805-3813, 2014 and “pKb werte”(http://www.periodensystem-online.de/index.php?sel=abc&prop=pKb-Werte&show=list&el=4&id=acid)

FIG. 6 depicts the percentage of lignin solubility for the commerciallyavailable purified Kraft lignin Amallin LPH and two alternativecommercially available purified Kraft lignins as a function of theequivalent mass ratio of base to lignin. The base used has a pKa ofgreater than or equal to 9.4.

FIG. 7 depicts the relative change in thickness swell as a function ofthe relative change in emulsifier loading for Kraft lignin,lignosulfonate, and a stearic acid-based emulsifier.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with one embodiment of the invention, there is providedlignin containing aqueous wax dispersions, their composition, methods ofmanufacture and use in the manufacture of composite wood panels. Inaccordance with another embodiment of the invention there is providedlignin containing aqueous wax emulsions, their composition, methods ofmanufacture and use in the manufacture of composite wood panels.

As used herein, the following terms will be understood to have thefollowing meanings.

“Composite wood panel”, or “panel”, as used herein, will be understoodto mean any form of wood or cellulosic material-based panel. “Compositewood panel” will be understood to include particleboard, fibreboard,such as medium density fibreboard (MDF) and high density fibreboard(HDF), flakeboard, chipboard, oriented strand board (OSB), waferboardand other similar products, wherein wood or cellulosic material is mixedwith adhesive and formed into a flat panel.

“Wood particles” will be understood to mean wood or lignocellulosicmaterial commonly used in manufacturing composite wood panels. This termwill, therefore, be understood to include wood particles, wood chips,wood shavings, wood wafers, wood strands, sawdust or other similarmaterials.

“Dispersion”, as used with respect to the present invention, will beunderstood to mean a composition comprising a continuous aqueous phaseand solid dispersed phase.

“Emulsion”, as used with respect to the present invention, will beunderstood to mean a composition comprising a continuous aqueous phaseand liquid dispersed phase. As known in the art, the term “emulsion” maybe used in the reverse, namely, to identify a liquid aqueous phasedispersed within a continuous non-aqueous phase. However, for thepurposes of the present description, the invention will generally bedescribed in terms of the former meaning.

“Wax” as used herein will be understood to mean any know waxes that aresuitable for use in manufacturing composite wood panels. For example,the wax component may comprise a natural wax, such as petroleum,vegetable, or animal derived waxes, or a synthetic wax. The petroleumwax may comprise a paraffin wax in the form of a scale wax or slack wax,as obtained from petroleum distillation processes. In addition, theinvention provides for the use of various natural waxes such asvegetable-based waxes. Thus, the invention may incorporate any wax orwax-like material that would normally be used in the art, orcombinations and mixtures thereof.

“Emulsifier” as used herein will be understood to be a surface activeagent (also called a “surfactant”) which lowers the surface tension ofthe medium in which it is dissolved, and/or lowers the interfacialtension with other phases. The emulsifier facilitates the formation ofan emulsion and increases the colloidal stability of the resultingemulsion of dispersion (IUPAC, Compendium of Chemical Terminology, 2nded. (the “Gold Book”) Compiled by A. D. McNaught and A. Wilkinson.Blackwell Scientific Publications, Oxford (1997)).

“Solids” or “solids content” as used herein will be understood to referto the amount (expressed as a weight percentage) of non-volatilematerial in the dispersion. More accurately, these terms refer to thetotal amount of non-volatile material that remains after evaporation ordrying to a constant weight.

“Lignin” as used herein refers to a “technical lignin” which comprises acomplex mixture of macromolecules consisting of coniferyl (guaiacyl),synapyl (synringyl), and p-coumaryl (p-hydroxyphenyl) repeat units,extracted from lignocellulosic materials such as wood. Importantphysiochemical properties of lignin such as the molecular weight, ashcontent, hydroxyl number, and so on vary with the process used toextract lignin.

“Kraft lignin” as used herein refers to a “technical lignin” that isextracted from wood using the Kraft pulping process. In particularexamples, the Kraft lignin is a purified Kraft lignin. The term“purified Kraft lignin” as used herein refers to a Kraft lignin whichhas been purified or extracted using the LignoBoost process (asdisclosed in WO2014 116150A1), or the LignoForce process (as disclosedin U.S. Pat. No. 9,091,023 B2), or other similar process. Examples ofcommercial sources of purified Kraft lignin include Amallin LPH™ andAmallin HPH™ from West Fraser, BioChoice™ from Domtar, Lineo from StoraEnso, and BioPiva from UPM.

The “equivalent lignin mass ratio” or “α” as used herein refers to theweight ratio of lignin and wax of the aqueous wax dispersion or aqueouswax emulsion. α=dry mass of lignin/mass of wax.

The “equivalent base mass ratio” or “β” as used herein refers to theweight ratio of base and lignin of the aqueous wax dispersion or aqueouswax emulsion. β=dry mass of base/dry mass of lignin.

The “equivalent solubilized lignin mass ratio” or “γ” as used hereinrefers to the weight ratio of solubilized lignin and wax of the aqueouswax dispersion or aqueous wax emulsion. γ=dry mass of solubilizedlignin/mass of wax.

It has been found that lignin and particularly purified Kraft lignin isa novel emulsifier that can be used in the preparation of aqueous waxdispersions or aqueous wax emulsions. Additionally, it has been foundthat the use of a lignin emulsifier and particularly a purified Kraftlignin emulsifier results in the production of aqueous wax dispersionsor aqueous wax emulsions that have superior properties as compared toaqueous wax dispersion or aqueous wax emulsions formed using emulsifierspreviously known in the art.

In particular, it has been found that compositions for an aqueous waxdispersion or an aqueous wax emulsion comprising lignin as theemulsifier are not hampered by the same trade-off between dispersionstability and performance in use as previously known emulsifiers. Ligninemulsifiers provide excellent stability even at low loading. Further ithas been found that increasing the lignin loading does not cause foamingof the aqueous wax dispersion. It has also been demonstrated that, forthe use in composite wood panels, aqueous wax dispersions from thisinvention have better water-repellent performance when compared to otherknown emulsifiers. Similar results are expected using aqueous waxemulsions.

Lignin generally refers to complex polyphenolic polymers formed fromconiferyl (guaiacyl), synapyl (synringyl), and p-coumaryl(p-hydroxyphenyl) repeat units. Lignin is extracted from lignocellulosicmaterial using a variety of industrial processes, such as kraft or sodapulping, sulphite pulping, bioethanol production, etc. Technical ligninisolated from these processes include Kraft lignin, soda lignin,lignosulfonates, organsolv lignin, etc. The lignin used in thisinvention preferentially comprises a purified form of lignin that can besolubilized in water. In a particular embodiment, the lignin is apurified form of lignin extract obtained from black liquor in the Kraftprocess.

Kraft lignin is extracted from black liquor as a by-product from theKraft pulping process. Kraft lignin can be further processed andpurified. Commercial processes have been developed for extracting andpurifying the Kraft lignin, generally involving acidification of theblack liquor using carbon dioxide followed by a coagulation stage,filtration and washing with acid and water. Examples of such processesare described in WO2014 116150A1 (“LignoBoost process”), or U.S. Pat.No. 9,091,023 B2 (“LignoForce process”). The resulting Kraft lignin isof high purity and can be suspended in water to form a Kraft ligninsuspension with a pH of 2-4.

For the purpose of acting as an emulsifier for aqueous wax dispersions,the Kraft lignin first needs to be solubilized. For example, Rojas andco-workers reported in “Lignins as Emulsion Stabilizers”, Chapter 12 ofMaterials, Chemicals, and Energy in Forest Biomass, 2007, pg. 182-199,that dissolved Kraft and soda lignins can be used as polymericamphiphiles for the stabilization of emulsions, but that theirperformance is heavily dependent on the pH. Without wishing to be boundto theory, it is believed that the solubility of Kraft lignin iscontrolled by the distribution of phenolic hydroxyl groups, and the pHof the medium. Kraft lignin contains a range of structurally similarguaiacyl and syringyl phenols that vary in pKa [see “pKa-values ofGuaiacyl and Syringyl Phenols Related to Lignin”, by Ragnar, M.;Lindgren, C. T. and Nilvebrant N.-O., J. Wood Chem. Technol. 2000,20(3), 277-305], giving rise to an approximate pKa of lignin rangingfrom 9.4 to about 10.8. Dissolution of Kraft lignin, i.e. deprotonationof its acidic form, can therefore only be achieved in the presence of asufficient quantity of a base of sufficient strength.

It has been found that for the purified Kraft lignin to act as anemulsifying agent for aqueous wax dispersions or aqueous wax emulsions,a complementary water-soluble base needs to be used.

Bases are well known in the art and are generally understood to becompounds that can accept a proton, as described in the Brønsted-Lowrytheory. A strong base is understood to be a base that fully dissociatesin water. A weak base is understood to be a base that partiallydissociates in water, the extent of which is described by the negativelog of the acid dissociation constant pKa.

The presence of the water-soluble base raises the pH of the medium,which results in the deprotonation of the phenolic hydroxyls and,subsequently, dissolution of the lignin macromolecule. Suitable basesfor solubilizing purified Kraft lignin include water-soluble strongbases. Other suitable bases for solubilizing purified Kraft lignininclude water-soluble weak bases with a pKa of approximately 9.4 orhigher. Still, other suitable bases for solubilizing purified Kraftlignin include water-soluble bases with a pKa of lower than 9.4. Varioussuch suitable water-soluble bases would be known to one of skill in theart. The amount of base required to achieve complete solubility of thepurified Kraft lignin is a function of the pKa of the base. As such,bases with a pKa of approximately 9.4 or higher are preferred, on thebasis that substantially less base is required to achieve completedissolution of the Kraft purified lignin macromolecules.

In one embodiment bases for the invention have a pKa of approximately9.4 and higher including potassium hydroxide, sodium hydroxide, andmonoethanolamine.

Without intending to be bound by theory, it may be consideredadvantageous to use a suitable volatile water-soluble base for thepurpose of the invention. The aqueous wax dispersions and aqueous waxemulsions disclosed herein may be used in the production of compositewood panel. The production of such composite wood panel typicallyinvolves hot pressing of the materials to form the panel. A volatilebase in its neutral form is likely to evaporate during hot pressing,thereby shifting the pH and acid-base equilibrium and driving purifiedKraft lignin to its water-insoluble and thus more hydrophobic state. Theterm “volatile base” as used to herein refers to an organic base thatcan evaporate under typical board pressing conditions used in theproduction of composite wood panels. Examples of volatile bases suitablefor this application include monoethanolamine, diethanolamine,triethanolamine, morpholine and aqueous ammonia.

The amount of a suitable water-soluble base required to solubilizelignin is expressed as the equivalent base mass ratio or β. A graphicalrepresentation of purified Kraft lignin solubility relative to β forvarious bases is shown in FIG. 4. For a particular purified Kraftlignin, the relative solubility can be expressed as a function of the pHor the equivalent base mass ratio β. For example, for a purified Kraftlignin produced by West Fraser (Amallin LPH™) and a water soluble basewith a pKa of approximately 9.4 or higher such as potassium hydroxide(pKa=15.1), sodium hydroxide (pKa=14.6), or monoethanolamine (pKa=9.45)the percentage solubility can be estimated by Equation 1:

%Solubility=[1/(0.01+0.99 exp(−150(β−0.006)))]  (Eq. 1)

It then follows from Equation 1, that a minimum equivalent base massratio or β min of 0.07 is required to fully solubilize this purifiedKraft lignin with a base with a pKa of approximately 9.4 or higher suchas potassium hydroxide, sodium hydroxide, or monoethanolamine. Morepreferably the base to lignin ratio of β≥0.10 is selected to fullysolubilize this purified Kraft lignin.

A graphical representation of the relative lignin solubility as afunction of the equivalent base mass ratio for potassium hydroxide andmonoethanolamine can be seen in FIG. 2.

Alternatively, for a purified Kraft lignin produced by West Fraser(Amallin LPH™) and a water soluble base with a pKa of lower than 9.4such as dimethylethanolamine (pKa=9.31), diethanolamine (pKa=8.96),methyldiethanolamine (pKa=8.54), or triethanolamine (pKa=7.73) thepercentage solubility is dependent upon the pKa of the base. Thecorrelation between the base pKa and the minimum equivalent base massratio β min can be approximated using a linear correlation as describedby Equation 2:

β min=−0.049*pKa+0.547   (Eq. 2)

It then follows from Equation 2, that the minimum equivalent base massratio β min can vary from 0.17 (pKa=7.73) to 0.095 (pKa=9.31).

A graphical representation of the minimum equivalent base mass ratio forvarious bases having different pKa is shown in FIG. 5.

Sodium carbonate having a pKa of 10.4 can be used to solubilize purifiedKraft lignin. However, sodium carbonate has been found in some cases tocause extremely high viscosity when used at an equivalent base massratio 0.07 or higher which may be detrimental in some circumstances.

It has further been found that aqueous wax dispersions prepared with thepurified Kraft lignin, Amallin LPH™, at an equivalent base mass ratio 3times the minimum equivalent base mass ratio were found to be unstable,indicating that there is a maximum equivalent base mass ratio.

The waxes that can be used in the formulations of the present inventionmay comprise any known waxes that are suitable for use in manufacturingcomposite wood panels. For example, the wax component of the aqueous waxdispersion or aqueous wax emulsion may comprise any natural wax, such aspetroleum, vegetable derived waxes, or animal derived wax such astallow, or any synthetic wax.

In one embodiment, the aqueous wax dispersion or aqueous wax emulsioncomprises a petroleum derived wax. In a particular example, the derivedpetroleum wax may comprise a paraffin wax in the form of a scale wax orslack wax, as obtained from petroleum distillation processes. In afurther embodiment, the wax has a melting point of about 45° C. to about90° C.

In another embodiment, the dispersion or emulsion comprises a vegetablederived wax. In a particular embodiment, the wax comprises hydrogenatedvegetable oil. Suitable hydrogenated vegetable oils include, but are notlimited to, hydrogenated soybean oil, hydrogenated palm oil,hydrogenated sunflower oil, hydrogenated canola oil, hydrogenated cornoil, hydrogenated olive oil, hydrogenated peanut oil, hydrogenatedsafflower oil or mixtures thereof. The use of vegetable based waxes isknown to have various economic and environmental advantages.

The solids content of the aqueous wax dispersions disclosed hereincludes wax, base, and lignin. Lignin and the base are preferentiallylocated in the aqueous continuous phase of the aqueous wax dispersion oraqueous wax emulsion.

Aqueous wax dispersions are kinetically stable, that is they demonstratestability only for a limited period of time after which the dispersionbreaks (i.e. the dispersion separates into a wax and aqueous phase). Theprocess by which an aqueous wax dispersion completely breaks isgenerally considered to be related to a change in the particle sizedistribution due to flocculation, resulting in creaming andsedimentation. Macroscopically, these processes are observed asstratification of the dispersion (creaming) or fallout of wax particles(sedimentation).

Aqueous wax emulsions are kinetically stable, that is they demonstratestability only for a limited period of time after which the emulsionbreaks (i.e. the emulsion separates into a liquid wax and aqueousphase). The process by which an aqueous wax emulsion breaks is generallyconsidered to be related to a change in the droplet size distributiondue to coalescence. Macroscopically, this process is observed asde-emulsification.

A stable aqueous wax dispersion is thus defined as a dispersion thatremains free from wax fallout for a period of at least 2 weeks.

An unstable aqueous wax dispersion is then defined as a dispersion thatdisplays wax fallout within a period of 2 weeks.

A stable aqueous wax emulsion is thus defined as an emulsion thatremains free from de-emulsification for at least 1 hour under gentileagitation.

An unstable aqueous wax emulsion is then defined as an emulsion thatdisplays de-emulsification within 1 hour under gentile agitation.

Stable aqueous wax emulsions and dispersions can be produced using alignin emulsifier, provided the absolute amount of lignin is sufficientto emulsify and stabilize the wax particles. For a purified Kraft ligninproduced by West Fraser (Amallin LPH™) and a water soluble strong basewith a pKa of approximately 9.4 or higher the absolute amount ofpurified Kraft lignin that is present in the aqueous phase as anemulsifier can then be described by Equation 3:

γ=α[1/(0.01+0.99 exp(−150(β−0.006)))]  (Eg. 3)

Stable aqueous wax emulsions and dispersions can be produced using alignin emulsifier using an equivalent solubilized lignin mass ratio of0.008<γ0.25. Preferentially, an equivalent solubilized lignin mass ratioof 0.01<γ0.10, more preferentially an equivalent solubilized lignin massratio of 0.01<γ0.04.

Aqueous wax dispersions produced in the presence of an insufficientamount of a suitable base contain insoluble lignin, which will settlefrom the aqueous wax dispersion under the force of gravity. Aqueous waxdispersions which contain insoluble lignin may not be suitable for allthe intended applications.

While not intending to be bound by theory, for some applications it maybe considered advantageous to only partially solubilize the lignin. Forexample, using a suitable base below the minimal equivalent base massratio 13 but in the presence of a sufficiently high equivalent ligninmass ratio a, the criterion for the equivalent solubilized lignin massratio y is met and an aqueous wax dispersion can be made. The insolublelignin present in the aqueous wax dispersion remains in its neutral andthus more hydrophobic form, which may provide a performance benefit inat least some of the intended applications of the invention.

As known in the art, different high shear mixing devices may be used toemulsify wax with the aqueous phase containing the lignin emulsifier toform a stable wax emulsion which may be used directly in or may be canbe cooled to a stable aqueous wax dispersion. The efficiency of the highshear mixing device is dependent on the energy provided to createsufficient inertial forces to overcome the surface tension forces.Commonly used high shear devices include rotor-stator mixers andhigh-pressure homogenizers. In both devices, a coarse emulsion of twoimmiscible liquids passes through a narrow gap, which causes highinertial forces that result in one of the liquid phases to break up insmall droplets. Another type of emulsification device is based onultrasonic cavitation, where high intensity ultrasound generatescavitation bubbles that, upon implosion, cause intensive shockwaves andhigh local velocities which can emulsify one liquid in another. Thesehigh shear mixing devices are commonly used to produce aqueous waxdispersions.

Yet another shear mixing device is based on hydrodynamic cavitation (aso-called liquid whistle), where a coarse emulsion of two immiscibleliquids at high pressure passes through a narrow orifice and over ablade, causing formation of cavitation bubbles that, upon implosion,cause intensive shockwaves and high local velocities which can emulsifyone liquid in another. An example of such as device is the Sonolator™ asproduced by Sonic Corporation.

The aqueous wax dispersions and aqueous wax emulsions of this inventioncan be produced using different high shear mixing devices, including theSilverson™ mixer (rotor-stator type), APV 31MR Lab Homogenizer(homogenizer type), and the Sonolator™ (hydrodynamic cavitation type).

When used in the manufacture of composite wood panels, aqueous waxdispersions and aqueous wax emulsions may be pumped, stored, sprayed,and potentially mixed with plant water, resin or other additives. Thesemanipulations demand a degree of resistance to shear (pumping andspraying), changes in electrolyte concentration (mixing), and foaming(pumping and storage).

When compared to the prior art, the aqueous wax dispersion and aqueouswax emulsion according to this invention provide one or more of thefollowing advantages:

A) Improved shear stability

B) Reduced foaming tendency and reduced foam persistence

C) Improved electrolyte stability

D) reduced effect on moisture repellent performance of wax, particularlyat higher emulsifier loading.

Aspects of the invention will now be described in terms of specificexamples. It will be understood that the purpose of all examplescontained herein is solely to illustrate the invention and that suchexamples are not intended to limit the invention in any way.

EXAMPLES

Lignin Sources

In one embodiment, black liquor obtained from the Kraft pulping processmay be used directly as the source of lignin. However, it has been foundthat the use of black liquor (obtained directly from Kraft process) asthe lignin source is less preferred because a) the black liquor has alow solids content requiring concentration of the material prior to itsuse, b) this material has a low lignin fraction and c) it contains othercontaminants such as salts and sugars which have been found todestabilize the wax dispersion in use.

In another embodiment the Kraft lignin is purified prior to use in theaqueous wax dispersions of the present application. Various sources ofcommercially available purified Kraft lignin were evaluated and werefound to be able to successfully stabilize an aqueous wax dispersion.FIG. 1 provides examples of commercially available purified Kraftlignins.

Solubilizinq Lignin

The fraction of soluble versus suspended, insoluble, purified Kraftlignin was determined by adding solid purified Kraft lignin powder tohot water at 80° C. containing a predetermined amount of a water-solublebase under vigorous agitation. The resulting mixture (20 w/w % solids)was agitated for 10 minutes, cooled, and any remaining suspendedpurified Kraft lignin allowed to settle under the force of gravity. Thefraction of soluble purified Kraft lignin was determined from a solidsreading of the clear aqueous layer (in duplicate).

FIG. 2 demonstrates that for a strong base, such as potassium hydroxide,a minimum equivalent base mass ratio β min is required to achievecomplete lignin solubility. Here, this minimum equivalent base massratio was determined to be approximately β min=0.07±0.01. This minimumequivalent base mass ratio was found to be the same for other strongbases such as sodium hydroxide and weak bases with a pKa ofapproximately 9.4 or higher such as monoethanolamine. For a weak basewith a pKa lower than approximately 9.4 the minimum equivalent base massratio varies with the pKa of the base. For dimethylethanolamine(pKa=9.31), diethanolamine (pKa=8.96), methyldiethanolamine (pKa=8.54),or triethanolamine (pKa=7.73) the minimum equivalent base mass ratioswere determined to be approximately β min=0.11±0.01, 0.10±0.01,0.14±0.01, and 0.17±0.01, respectively. A graphical representation oflignin solubility relative to β for various bases is shown in FIG. 4.

Purified Kraft lignin Emulsifier

Standard Procedure: Aqueous wax dispersions were prepared using thefollowing standard procedure. Emulsifying molten wax with an aqueousphase containing the water-soluble base and purified Kraft lignin.First, the molten wax and aqueous phase are emulsified under high shearto form a coarse emulsion. Second, the coarse emulsion is passed througha high-shear homogenizer to form a fine emulsion. Finally, the fineemulsion is cooled quickly to below the wax congealing point to form thefinal aqueous wax dispersion.

Following the standard procedure described above, but in the absence oflignin, no aqueous wax dispersion is formed, and the coarse emulsionformed under high shear immediately breaks once shearing is stopped.

Again, following the standard procedure, but in the absence of awater-soluble base, the coarse emulsion formed under high shearimmediately breaks once shearing is stopped. This example demonstratesthat in the absence of a water-soluble base no aqueous wax dispersioncan be formed, and that under those conditions the purified Kraft lignindoes not function as a suitable emulsifier.

In the presence of a suitable water-soluble base that is below theminimal equivalent base mass ratio, an aqueous wax dispersion may beformed using the standard procedure described above, but only if asufficient amount of purified Kraft lignin is dissolved in the aqueousphase. However, as the insoluble purified Kraft lignin settles, thisaqueous wax dispersion may be unsuitable for use in the intendedapplication for the manufacture of composite wood panels.

In the presence of a suitable water-soluble base having a pKa ofapproximately 9.4 or higher that is at or above the minimal equivalentbase mass ratio (β>0.07), an aqueous wax dispersion is formed using thestandard procedure described above. However, only if the absolute amountof dissolved purified Kraft lignin is sufficient. The resulting aqueouswax dispersion is stable and homogeneous in appearance.

In the presence of a suitable water-soluble base having a pKa of lowerthan 9.4 that is at or above the minimal equivalent base mass ratio βmin for that particular base, an aqueous wax dispersion may be formedusing the standard procedure described above. However, only if theabsolute amount of dissolved purified Kraft lignin is sufficient. Theresulting aqueous wax dispersion is stable and homogeneous inappearance.

Table 1 describes aqueous wax dispersions made using various bases ofdiffering pKa.

Solubility at β = pKa pKa 0.10 β_(min) Stable Base Abbr. [—] Reference[%] [—] Dispersion Triethanolamine TEA 7.73 1 66 0.17 YesMethyldiethanolamine MDEA 8.54 1 90 0.14 Yes Diethanolamine DEA 8.96 199 0.10 Yes Dimethylethanolamine DMEA 9.31 1 99 0.11 YesMonoethanolamine MEA 9.45 1 100 0.08 Yes Sodium Carbonate SC 10.4 2 1000.07 Yes Potassium Hydroxide KOH 15.1 2 100 0.07 Yes Sodium HydroxideNaOH 14.56 2 100 0.07 Yes Reference: 1. Rayer, A. V., Sumon, K. A.,Jaffari L/and Henni, A., Dissociation constants (pKa) of tertiary andcyclic amines: Structural and temperature dependencies, Journal ofChemical and Engineering Data 59(11) 3805-3813, 2014. 2. “pKb Werte”http://www.periodensystem-online.de/index.php?sel=wertdesc&prop=pKb-Werte&show=list&el=92&id=acid

Meeting the requirements specified in the above listed scenarios, aequivalent lignin mass ratio comprising 0.008 to 0.25 can be utilized toform an aqueous wax dispersion using the procedure described above. Aequivalent lignin mass ratio α<0.008, for example β=0.005, results in afine emulsion that breaks during cooling. (A flow chart depicting thevarious scenarios described above is shown in FIG. 3.)

The standard procedure described above, has been carried out using thepurified Kraft lignin Amallin LPH™ (from producer West Fraser, producedusing the LignoForce process) to successfully produce stable aqueous waxdispersions. Amallin LPH™ was fully solubilized using potassiumhydroxide at an equivalent base mass ratio β of 0.10, and, subsequently,used to emulsify Prowax 512™ at an equivalent lignin mass ratio α of0.04. The final properties of the aqueous wax dispersion were measuredas follows: solids=47.9%, viscosity=23 cP, and pH=11.2. Similar resultshave been obtained substituting other commercially available sourcespurified Kraft lignin for the Amallin LPH™. A graphical representationof the purified Kraft lignin solubility as a function of equivalent basemass ratio is provided in FIG. 6 including the results for Amallin LPHand the additional commercial sources which are identified asAlternative 1 and Alternative 2.

Again, following the standard procedure described above, various typesof waxes have been successfully used to produce stable aqueous waxdispersions, using Amallin HPH™ (West Fraser) as an emulsifier asdemonstrated in Table 2 below.

TABLE 2 α B Solids Viscosity pH Wax Type Source [—] [—] [%] [cP] [—]Purewax ™ Paraffin Petroleum 0.07 0.15 49.2 55 9.1 slack Prowax ™ 460Paraffin Petroleum 0.07 0.15 49.9 32 9.5 slack Prowax ™ 515 ParaffinPetroleum 0.07 0.15 49.8 34 10.2 slack SCP 125 Natural Hydrogenated 0.070.15 50.1 279 9.7 Tallow KENWAX  ® Slack Petroleum 0.07 0.15 50.9 4711.4 MNSW SX 50 Synthetic Fisher 0.07 0.15 49.4 24 9.7 Tropsch

Dispersion Stability

Aqueous wax dispersions were subjected to three aqueous wax dispersionstability tests, as described below.

1) Shear stability test—Shear was applied to the aqueous wax dispersionusing a Silverson L4R high-shear mixer at 8000 rpm. Shearing wascontinued until the aqueous wax dispersion breaks, or until the meltingpoint of the wax is exceeded (at which point a wax emulsion is formedwhich will not break). The shear stability of the aqueous wax dispersionis expressed as the time until the wax dispersion breaks and thetemperature that corresponds to that time point.

2) Foaming tendency and foam stability—100 mL of wax dispersion isplaced inside a 250 mL graduated cylinder and manually shaken with ahorizontal motion with an amplitude of 70 cm for 60 seconds. Thecylinder is then placed on a horizontal surface. Immediately, thedifference between the liquid meniscus and the surface of the foam isrecorded, which numerically expresses the foaming tendency. Thisdifference is recorded again after 5 minutes, which numericallyexpresses the foam stability or foam persistence.

3) Salt stability—a 100 mL 4.5 M sodium chloride solution is graduallyadded to a 250 g sample of aqueous wax dispersion under medium agitationuntil the aqueous wax dispersion breaks. The salt stability of theaqueous wax dispersion is expressed as the amount of sodium chlorideadded up to the point where the aqueous wax dispersion breaks.

The aqueous wax dispersions according to the application have beencompared to aqueous wax dispersions made using conventional emulsifierssuch as sodium lignosulfonate, stearic acid, and behenic acid atcommercially relevant levels. The results are shown in the Table 3below:

TABLE 3 Shear Shear Foaming Foam Salt Emulsifier α Visc StabilityStability Tendency Persistence Stability [%] [—] [cP] [sec] [° C.] [mL][mL] [mmol] Amallin LPH ™ 0.4 0.008 21  5 24 N/A N/A N/A Amallin LPH ™0.5 0.01 17  30 25 0 0 DNB Amallin LPH ™ 1.0 0.02 19 DNB >80 0 0 DNBAmallin LPH ™ 1.5 0.03 25 DNB >80 0 0 DNB Amallin LPH ™ 10.0 0.25 200DNB >80 0 0 DNB Lignosulfonate 2.0 — 23  30 27 0 0 DNB Lignosulfonate4.0 — 36 260 42 0 0 DNB Stearic Acid 1.8 — 118 241 42 27 24 72 StearicAcid 3.6 — 276 DNB >80 28 20 114 Behenic Acid 1.1 — 26 300 53 0 0 21Behenic Acid 2.2 — 50 DNB >80 0 0 85 * DNB = wax dispersion does notbreak; N/A = measurement could not be performed due to the low shearstability of the aqueous wax dispersion; all aqueous wax dispersionsprepared at 50% solids using the same wax and produced using the processdescribed above.

Table 3 demonstrates the unexpected advantage of using purified Kraftlignin as the emulsifier for aqueous wax dispersions. First, the aqueouswax dispersion has excellent shear stability at any lignin loading >1.0%(α=0.02), and does not break as the wax dispersion temperature exceedsthe melting point of the wax. In comparison, a substantially higheremulsifier loading is required for the soap-based wax dispersions, whichall break before the wax melting point temperature is reached.

Second, the aqueous wax dispersion of this invention has little to notendency to foam. This is particularly apparent in comparison to somesoap-based wax dispersions which generally display significant foamingtendency and a strong foam persistence.

Third, the aqueous wax dispersion has excellent salt stability and doesnot break as the total amount of salt solution is added. This iscontrary, to the soap-based wax dispersions which all break upon theaddition of salt.

Emulsion Stability

Aqueous wax emulsions were prepared using the following standardprocedure. Emulsifying molten wax with an aqueous phase containing thewater-soluble base and purified Kraft lignin. The molten wax and aqueousphase are emulsified under high shear to form a coarse emulsion. Second,the coarse emulsion is passed through a high-shear homogenizer to form afine emulsion. Finally, the fine emulsion is kept at a temperature abovethe congealing point of the wax and under gentle agitation for at leastone hour. All of the wax emulsions were prepared at 50% solids contentusing the same wax and produced using the process described above.

The aqueous wax emulsion stability is monitored visually for 1 hour forsigns of (1) coalescence, or (2) lignin precipitation. Coalescence isdefined as a reversible separation of the fine emulsion into two layersof which one is concentrated, and one is diluted in wax content (i.e.the fine emulsion is not longer homogeneous throughout). Ligninprecipitation is defined as the presence of solid purified Kraft ligninparticles in the fine emulsion (i.e. undissolved purified Kraft lignin).

Aqueous wax emulsions according to the application were prepared atdecreasing equivalent lignin mass ratio. The results are shown in theTable 4 below:

TABLE 4 Wax Emulsifier α Emulsion Lignin [%] [—] Stability coalescenceprecipitation 10 0.25 Stable No No 1.0 0.02 Stable No No 0.50 0.01Stable No No 0.40 0.008 Stable No No 0.20 0.004 Stable No No 0.10 0.002Stable No No 0.0 0.0 Not Stable Yes No

The results in Tables 3 and 4 demonstrate that a stable aqueous waxemulsion can be made using purified Kraft Lignin at equivalent ligninmass ratios considerably lower than the minimal equivalent lignin massratio of 0.008 determined for manufacture of a stable aqueous waxdispersion.

Composite Wood Panel Manufacture

Panel Manufacture Example 1

Monolayer particleboard panels were pressed using Douglas Fir core woodchips. The panels were consolidated in a hot press at 174° F. to adimension of 22″×22″, a thickness of 0.5″, and a target density of 40lbs/cuft. A liquid melamine urea formaldehyde resin (1.05MR from Arclin)was used at 6% loading and a press factor of 14 s/mm. All waxdispersions were used at 1% loading. The consolidated panels wereconditioned for 2 weeks and tested in accordance with ASTM D1037 - 12.The results for panel density and thickness swell are shown in Table 5.

TABLE 5 Emulsifier Loading Density 2 hr TS 8 hr TS 24 hr TS Emulsifier[%] [lbs/cuft] [%] [%] [%] Amallin LPH/ 1.5 45.4 (0.8) 7.0 (0.4) 11.6(0.6) 20.3 (0.9) KOH Amallin LPH/ 10.0 45.5 (1.0) 6.3 (0.7) 12.2 (1.0)19.5 (1.6) KOH Amallin LPH/ 1.5 43.4 (1.2) 6.7 (0.6) 11.9 (1.3) 18.7(1.1) NaOH Amalin LPH/ 1.5 45.2 (2.8) 6.9 (1.1) 10.2 (1.6) 18.5 (1.8)MEA Stearic Acid 1.5 42.3 (1.9) 6.4 (0.4) 11.8 (0.8) 18.5 (1.0) BehenicAcid 1.2 43.6 (0.3) 6.9 (1.1) 10.3 (1.6) 18.5 (1.8) TS = thickness swell

Table 5 discloses that aqueous wax dispersions of this invention havecomparable moisture repellent properties when compared to waxdispersions based on commercially available soap-based emulsifiers. Inthis example the performance of the wax appears unaffected by asubstantial increase in the amount of purified Kraft lignin emulsifierused.

Panel Manufacture Example 2

Monolayer particleboard panels were pressed using particleboard woodchips. The panels were consolidated in a hot press at 390° F. to adimension of 9″×9″, a thickness of 0.5″, and a target density of 44lbs/cuft. A powdered phenol formaldehyde resin (from GP Resins) was usedat 10% loading. All wax dispersions were used at 1% loading. Theconsolidated panels were conditioned overnight and tested in accordancewith ASTM D1037 -12. The results for panel density and thickness swellare shown in Table 6.

TABLE 6 Emulsifier TS/ Loading Density 24 hr TS 24 hr WA Rel. 24 hr TSLoading Rel. 24 hr WA [%] [lbs/cuft] [%] [%] [%] [%/%] [%] Amallin LPH1.0 713 (17) 7.34 (0.28) 23.2 (0.8) 100 100 Amallin LPH 4.5 706 (14)8.93 (0.72) 29.7 (1.5) 122 0.049 127 Stearic Acid 1.0 707 (14) 6.23(0.67) 21.0 (1.8) 100 100 Stearic Acid 4.5 703 (19) 8.88 (0.68) 30.5(0.6) 143 0.096 146 Lignosulfonate 4.0 723 (27) 8.12 (0.90) 24.0 (0.2)100 100 Lignosulfonate 8.0 694 (6)  9.99 (0.34) 33.1 (1.8) 123 0.115 138TS = thickness swell; WA = Water absorbance

Table 6 discloses that moisture repellent performance of aqueous waxdispersions of this invention are significantly less affected by achange in the emulsifier loading when compared to aqueous waxdispersions based on commercially available soap-based emulsifiers. Theaqueous wax dispersions of the application thus combine excellentaqueous wax dispersion stability without compromising moisture repellentperformance of wax in composite wood panels. From the table it can beobserved that there is no statistical difference between emulsifiers atlow emulsifier loading. It should be noted that for lignosulfonate aminimum 4% loading is needed to make emulsion stable wax dispersion andit is therefore not possible to increase the amount of lignosulfonate by450%. The lignosulfonate was increased by only 200% rather than the 450%increase for the other emulsifiers. By comparing the thickness swellincrease relative to emulsifier increase it is apparent that purifiedKraft lignin (Amallin LPH) has the least impact on thickness swell. FIG.7 is a graphical representation of the effect of emulsifier loading forKraft lignin, stearic acid and lignosulfonate on the change in thicknessswell.

Manufacturing methods can vary widely depending on the product andprocess used and would be familiar to one of skill in the art. In thecase of medium density fiberboard, for example, the aqueous waxdispersion may be added just prior to the pressurized refiner. The fiberis then dried, formed into a mat, and pressed into the final productusing a continuous or multi-opening press. In the case of particle boardor OSB, the aqueous wax dispersion is typically added directly to theblender. Other methods will be known to a person of skill in the art.

Although the invention has been described with reference to certainspecific embodiments, various modifications thereof will be apparent tothose skilled in the art without departing from the purpose and scope ofthe invention as outlined in the claims appended hereto. Any examplesprovided herein are included solely for the purpose of illustrating theinvention and are not intended to limit the invention in any way. Anydrawings provided herein are solely for the purpose of illustratingvarious aspects of the invention and are not intended to limit theinvention in any way. The disclosures of all prior art recited hereinare incorporated herein by reference in their entirety.

We claim:
 1. An aqueous wax emulsion or dispersion or comprising: wax;water and an emulsifier, wherein the emulsifier comprises lignin; and awater-soluble base; and wherein, solubility of the lignin is achievedthrough the addition of base.
 2. The aqueous wax emulsion or dispersionof claim 1, wherein the lignin is a Kraft lignin that can be solubilizedin water.
 3. The aqueous wax emulsion or dispersion of claim 1 whereinthe lignin is purified Kraft lignin wherein the purification is by aLignoForce or LignoBoost process.
 4. The aqueous wax emulsion ordispersion of claim 1, wherein the water-soluble base is selected fromthe groups consisting of mono-functional amines, multi-functionalamines, alkali metal salts, alkaline earth metal salts and combinationsthereof.
 5. The aqueous wax emulsion or dispersion of claim 1 whereinthe water-soluble base is added in an amount sufficient to dissolve thelignin and the amount of base is determined by the acid dissociationconstant (pKa) of the base.
 6. The aqueous wax emulsion or dispersion ofclaim 1 wherein the base has a pKa≥9.4.
 7. The aqueous wax emulsion ordispersion of claim 6 wherein the base is potassium hydroxide, sodiumhydroxide or monoethanolamine,
 8. The aqueous wax emulsion or dispersionof claim 7 wherein the minimum equivalent base mass ratio is about 0.07.9. The aqueous wax dispersion of claim 1 wherein the base has a pKa<9.4.10. The aqueous wax emulsion or dispersion of claim 9 wherein the baseis diethanolamine or triethanolamine.
 11. The aqueous wax emulsion ordispersion of claim 10 wherein the minimum equivalent base mass ratio isin the range of 0.17 to 0.095.
 12. The aqueous wax emulsion ordispersion of claim 1 wherein the base is a volatile base.
 13. Theaqueous wax emulsion or dispersion of claim 1 wherein the hydrocarbonwax is paraffin slack wax, refined paraffin wax, Fisher Tropsch wax,polyethylene wax, synthetic wax, natural wax, or mixtures thereof. 14.The aqueous wax emulsion or dispersion of claim 13 wherein thepolyethylene wax is oxidized polyethylene wax or maleated polyethylenewax,
 15. The aqueous wax emulsion or dispersion of claim 13 wherein thenatural wax is a vegetable wax or animal fat.
 16. The aqueous waxemulsion or dispersion of claim 1 wherein equivalent solubilized ligninmass ratio is greater than 0.008 and less than or equal to 0.25.
 17. Theaqueous wax emulsion or dispersion of claim 16 wherein the equivalentsolubilized lignin mass ratio is greater than 0.01 and less than orequal to 0.1.
 18. The aqueous wax emulsion or dispersion of claim 17wherein the equivalent solubilized lignin mass ratio is greater than0.02 and less than or equal to 0.04.
 19. The aqueous wax emulsion ordispersion of claim 1 wherein the equivalent lignin mass ratio isgreater than 0.5.
 20. The aqueous wax emulsion or dispersion of claim 19wherein the equivalent lignin mass ratio is less than 0.25
 21. Theaqueous wax emulsion or dispersion of claim 1 wherein the wax comprisesbetween 20 wt % to 60 wt % of the total solids of the aqueous waxdispersion.
 22. The aqueous wax emulsion of claim 1 wherein theequivalent solubilized lignin mass ratio is greater than 0.002 and lessthan or equal to 0.25.
 23. A method of preparing an aqueous wax emulsionaccording to claim 1 comprising: i) preparing an aqueous phasecontaining an emulsifier comprising lignin and water-soluble base; ii)emulsifying molten wax with the aqueous phase and iii) optionallystoring the emulsion at a temperature above the congealing temperatureof the wax with agitation.
 24. A method of preparing an aqueous waxdispersion according to claim 1 comprising: i) preparing an aqueousphase containing an emulsifier comprising lignin and water-soluble base;ii) emulsifying molten wax with the aqueous phase and iii) cooling tobelow the wax melting temperature to form the aqueous dispersion. 25.The method according to claim 23 wherein the emulsifying step comprises,first, emulsifying under high shear to form a coarse emulsion andsecond, passing the coarse emulsion through a high shear homogenizer toform a fine emulsion.
 26. The method according to claim 24 wherein theemulsifying step comprises, first, emulsifying under high shear to forma coarse emulsion and second, passing the coarse emulsion through a highshear homogenizer to form a fine emulsion.
 27. Use of an aqueous waxemulsion or dispersion according to claim 1 in the manufacture ofcomposite wood panels.
 28. A method of manufacturing a composite woodpanel comprising the steps of (i) resinating lignocellulosic material inthe presence of an adhesive resin and an aqueous wax emulsion ordispersion as defined in claim 1, (ii) forming the resinatedlignocellulosic material containing adhesive and aqueous wax dispersion,and (iii) consolidating the formed lignocellulosic material usingpressure and temperature.